Yes, I have done something similiar to this in v0.9 using a custom theme and GDI's DrawString method.

Assign a custom theme then load the interstate from the FeatureDataSet. Next load your shield as a bitmap and draw the interstate number on the bitmap and then assign the new bitmap as the symbol to the returned style.

I have actually been considering doing this for Interstate shields. For performance sake I might opt to actually have a predefined shield for each route. You could even programattically generate your shield bitmaps from your data and store them
as static images. Then you would just load the appropriate bitmap in your custom theme instead of drawing the route number dynamically. The dynamic method is possible though, I am doing it already with things that are more dynamic than route numbers.

You will need to use a VectorLayer. You will also need a seperate datasource with point locations for the shields. I will try to get you some sample code for the CustomTheme and DrawString methods this week.